With the development of medical technology and the improvement of living standards, the average lifespan of a human has been almost doubled over the past half century, and thus the ratio of the elderly population to the total population has increased rapidly. Along with the development of an aging society, senile dementia has emerged as one of the major health problems that need to be addressed in the twenty-first century. Therefore, the need to develop functional materials, foods, etc. that can prevent and treat cognitive impairments including dementia has been increasing.
Dementia that is a typical disease of cognitive impairments is a pathological condition that needs to be distinguished from normal aging and is classified into Alzheimer's disease, vascular dementia, and other dementias caused by alcoholism, trauma, sequelae of Parkinson's disease, etc.
It has been reported that Alzheimer's disease is one of chronic psychiatric disorders including disorders of higher cerebral functions such as loss of memory, impaired consciousness, spatiotemporal chaos, thinking ability, arithmetic ability, judgment, common sense, etc. Moreover, it has been reported that Alzheimer's disease also occurs in relatively young people and most frequently occurs in elderly people as the incidence is increased two times for each increase of 5 years in the range of 65 to 85 years old. While the pathogenesis of Alzheimer's disease is not clearly known, a decrease in acetylcholine function in the central nervous system most commonly occurs, and thus therapeutic methods of administering acetylcholine precursors or drugs that inhibit the degradation of acetylcholine to increase the concentration of acetylcholine in the brain have been used. Therefore, acetylcholinesterase (hereinafter, ‘AChE’) inhibitors have been used alone or in combination with existing cholinesterase inhibitors, and examples of such drugs include tacrine, donepezil, rivastigmine, galantamine, etc. While these drugs are acetylcholinesterase inhibitors, they only slow the progression of diseases, but have little effect on the treatment and have limited therapeutic potential at the beginning of the disease, and thus made efforts have been made to develop drugs that treat the underlying cause of Alzheimer's disease (Terry and Buccafusco, 2003; Kar et al., 2004; Akhondzadeh et al., 2008; Cummings et al., 2008; Voss et al., 2008).
Vascular dementia is mostly caused by damage to the brain cells due to lack of blood supply to certain parts of the brain caused by cerebral arteriosclerosis. The causes of the vascular dementia and Alzheimer's disease are different, but they are the same in that they cause damage to memory and learning ability.
Accordingly, the present inventors have studied to develop an effective medicine for prevention or treatment of cognitive impairments such as dementia and found herbal extracts and their active ingredients which can effectively improve memory and learning ability, thus completing the present invention.